At the heart of many computer systems is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating, but when the disk rotates air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the reading and writing functions.
The write head includes at least one coil, a write pole and one or more return poles. When current flows through the coil, a resulting magnetic field causes a magnetic flux to flow through the write pole, which results in a magnetic write field emitting from the tip of the write pole. This magnetic field is sufficiently strong that it locally magnetizes a portion of the adjacent magnetic media, thereby recording a bit of data. The write field then travels through a magnetically soft under-layer of the magnetic medium to return to the return pole of the write head.
A magnetoresistive sensor such as a Giant Magnetoresistive (GMR) sensor, a Tunnel Junction Magnetoresistive (TMR) sensor or a scissor type magnetoresistive sensor can be employed to read a magnetic signal from the magnetic media. The magnetoresistive sensor has an electrical resistance that changes in response to an external magnetic field. This change in electrical resistance can be detected by processing circuitry in order to read magnetic data from the magnetic media.
The magnetic media can be a perpendicular magnetic recording media that can include a magnetic recording layer that has an easy axis of magnetization oriented substantially perpendicular to the substrate. Hexagonal Close Packed (HCP) Co-alloys can be used as the magnetic recording layer for such perpendicular magnetic recording. The easy axis of magnetization for these materials lies along the c-axis or [0001] direction.
A perpendicular magnetic recording media is generally formed on a substrate with a soft magnetic under-layer (SUL), one or more inter-layers, and a perpendicular magnetic recording layer, and may include a cap layer exchange coupled with the magnetic recording layer. The soft magnetic under-layer (SUL) serves to concentrate a magnetic flux emitted from a main magnetic pole of the magnetic write head during recording on the magnetic recording layer. The inter-layers (also referred to as seed layers) serve to control the size of magnetic crystal grains and the orientation of the magnetic crystal grains in the magnetic recording layer. The inter-layers also serve to magnetically de-couple the magnetically soft under-layer and the magnetic recording layer. The magnetic recording layer is the layer in which a bit of data is stored based on the orientation of the magnetization of individual magnetic grains.
Because the magnetic recording layer has a magnetization that is oriented parallel to magnetic fields used to write to the media, reversing the magnetization of the magnetic recording layer may be difficult. To assist in reversing the magnetization of the magnetic grains in the magnetic recording layer, the magnetic media may also include a cap layer that is exchange coupled to the magnetic recording layer. The cap layer is typically formed from a CoPt alloy such as CoPt, CoPtCr, CoPtCrB, etc. The cap layer may directly contact the magnetic recording layer, or a coupling layer may be fabricated between the cap layer and the magnetic recording layer. When a coupling layer is used, the structure is sometimes referred to as an exchange spring structure.
As the areal bit density of a magnetic recording media increases, the magnetic regions in the magnetic recording layer become smaller. This may reduce the read signal generated in a read head of the magnetic recording system. One solution to improve the read signal is to reduce the thickness of the carbon overcoat that is typically applied over the cap layer. The carbon overcoat is a non-magnetic layer applied to the top of the cap layer to protect the media from corrosion and/or damage. Reducing the thickness of the carbon overcoat reduces the relative distance between the read head and the cap layer. However, as the carbon overcoat becomes thinner, the corrosion resistance of the disk may degrade, especially if the overcoat is rough.
Another solution for improving the read signal is to reduce the clearance between the read head and the top surface of the disk. However, one consequence of a reduced clearance is head-to-disk contact, which is undesirable. Head-to-disk contact occurs when the slider on which the read and write heads are formed makes contact with the disk. Head-to-disk contact can cause damage to the slider, the disk or both. It therefore, remains an ongoing challenge to improve the performance of the magnetic media.